Solid state image sensor

ABSTRACT

A solid state image sensor has a plurality of ranging pixels on the imaging area thereof and each of the ranging pixels has a photoelectric conversion section and an optical waveguide arranged at the light-receiving side of the photoelectric conversion section. The optical waveguide has at least two optical waveguides including a first optical waveguide arranged at the light-receiving side and a second optical waveguide arranged at the side of the photoelectric conversion section in the direction of propagation of light. The core region of the first optical waveguide shows a refractive index lower than the refractive index of the core region of the second optical waveguide and is designed so as to show a high light-receiving sensitivity relative to light entering at a specific angle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid state image sensor. Moreparticularly, the present invention relates to a solid state imagesensor to be used in a digital still camera, a digital video camera orthe like.

2. Related Background Art

Distance measurement techniques for auto-focusing (AF) operations ofdigital still cameras and digital video cameras are known. With regardto such distance measurement techniques for AF operations, U.S. Pat. No.6,829,008 proposes a solid state image sensor having some of its pixelsprovided with a distance measuring function and adapted to measuredistances by way of phase detection.

Phase detection is a technique of measuring a distance by comparing theimages of light passing through different regions on the pupil of acamera lens and measuring the distance by triangular surveying by meansof stereo images.

This technique realizes high speed and high precision AF because thetechnique does not require any operation of moving a lens for measuringa distance unlike conventional contrast measurement.

It also realizes real time AF when picking up a moving image.

According to U.S. Pat. No. 6,829,008, an aperture is formed between themicrolens and the photoelectric conversion section of a solid stateimage sensor at a position eccentric relative to the optical center ofthe microlens. With this arrangement, light passing through specificregions on the pupil of a camera lens can be selectively led to thephotoelectric conversion section.

However, the above-described arrangement of an aperture at an eccentricposition according to U.S. Pat. No. 6,829,008 may not necessarily besatisfactory for improving the accuracy of distance measurement becausefluxes of light cannot be separated sufficiently due to scattering oflight at the wiring section of the solid state image sensor.

Additionally, a problem as pointed out below can arise when thearrangement of U.S. Pat. No. 6,829,008 is applied to a small solid stateimage sensor having a small pixel size.

As the pixel size is reduced, the F value of the microlens for leadinglight to the photoelectric conversion section increases to make the sizeof diffraction image substantially equal to the pixel size.

Then, light expands in pixels and fluxes of light cannot be separatedsufficiently at the eccentric aperture so that the obtained results maynot necessarily be satisfactory for improving the accuracy of distancemeasurement.

SUMMARY OF THE INVENTION

In view of the above-identified problem, an object of the presentinvention is to provide a solid state image sensor that can highlyprecisely measure distances even when its pixel size is small.

According to the present invention, the above object is achieved byproviding a solid state image sensor having a plurality of rangingpixels on the imaging area thereof, each of the ranging pixels having aphotoelectric conversion section for converting light into an electricsignal and an optical waveguide including a core region and a cladregion arranged at the light-receiving side of the photoelectricconversion section; the optical waveguide having at least two opticalwaveguides including a first optical waveguide arranged at thelight-receiving side and a second optical waveguide arranged at the sideof the photoelectric conversion section in the direction of propagationof light; the core region of the first optical waveguide showing arefractive index lower than the refractive index of the core region ofthe second optical waveguide and designed so as to show a highlight-receiving sensitivity relative to light entering at a specificangle.

Thus, the present invention can realize a solid state image sensor thatcan highly precisely measure distances even when its pixel size issmall.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a ranging pixel arrangedat a part of the solid state image sensor according to a firstembodiment of the present invention.

FIG. 2 is a graphic illustration of the angle of incidence dependency ofthe light-receiving sensitivity of the pixels of the first embodiment.

FIG. 3 is a schematic illustration of the method of measuring thedistance to a subject by means of the image sensor of the firstembodiment.

FIG. 4 is a schematic cross-sectional view of a ranging pixel arrangedin a part of the solid state image sensor of the first embodimentshowing the numerical example described below for the first embodiment.

FIG. 5 is a graphic illustration of the angle of incidence dependency ofthe light-receiving sensitivity of the pixels of the first embodimentshowing the numerical example described below for the first embodiment.

FIG. 6 is a schematic cross-sectional view of a ranging pixel arrangedat a part of the solid state image sensor according to a secondembodiment of the present invention.

FIGS. 7A, 7B, 7C, 7D, 7E, 7F and 7G are schematic illustrations of theprocess of manufacturing the solid state image sensor according to athird embodiment of the present invention and having a ranging pixel asshown in FIG. 1.

FIG. 8 is a schematic illustration of a digital camera loaded with asolid state image sensor according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A solid state image sensor according to the present invention canmeasure distances highly precisely as described above even when thepixel size is small. The present invention is made by paying attentionto a phenomenon that the light propagation state (guided mode) in apixel varies as a function of the angle of incidence of light enteringthe optical waveguide arranged in the pixel.

More specifically, the optical waveguide is formed in at least twostages in the direction of propagation of light and the refractive indexof the core region at the light-receiving side is made lower than therefractive index of the core region at the side of the photoelectricconversion section.

With this arrangement, a solid state image sensor that can measuredistances highly precisely is realized as a result of improving thelight-receiving sensitivity relative to light entering at a specificangle and making light passing through a specific region on the pupil ofa lens to be selectively received.

Now, the present invention will be described in greater detail below byreferring to the accompanying drawings that illustrate embodiments ofsolid state image sensor according to the present invention. Throughoutthe drawings, the components having the same functions are denoted bythe same reference numerals and will not be described repeatedly.

Now, the embodiments of the present invention will be described.

First Embodiment

The configuration of the solid state image sensor according to the firstembodiment of the present invention will be described below by referringto FIG. 1.

FIG. 1 illustrates a pixel 100 arranged in a part of the solid stateimage sensor of this embodiment and having a distance measuringfunction.

Light 101 entering the pixel 100 is propagated through the first opticalwaveguide 102 (the first core region 112, the first clad region 122) andthe second optical waveguide 103 (the second core region 113, the secondclad region 123).

Propagated light is absorbed by photoelectric conversion section 104 andconverted into an electric signal. Note, however, that the photoelectricconversion section 104 is electrically controlled by means of metalwiring 106, gate electrode 107 and so on.

The first optical waveguide 102 operates in various guided modes forcoupling that differ to correspond to the angles of incidence of lightentering it.

Therefore, when light enters the first optical waveguide with aplurality of angles of incidence at a same time, it is coupled todifferent guided modes that differ to correspond to the angles ofincidence and propagated in the optical waveguide 102 in differentguided modes.

Then, as light is propagated in the optical waveguide 102 in differentguided modes, the electromagnetic field modes are spatially separated inthe optical waveguide.

A light shielding member 105 and a second optical waveguide 103 arearranged at the light exit end of the first optical waveguide 102 inorder to selectively detect the spatially separated electromagneticfield modes in the photoelectric conversion section 104.

With this arrangement, the light shielding member 105 has a function ofselectively shielding incident light at angle of incidence −θ (in thefirst direction) and blocking light entering the photoelectricconversion section 104.

On the other hand, the second optical waveguide 103 has a function ofselectively and efficiently guiding incident light at angle of incidence+θ (in the second direction) to the photoelectric conversion section104.

With the above-described arrangement, the photoelectric conversionsection 104 can be made to show a light-receiving sensitivity relativeto incident light that differs between the angle of incidence −θ (thefirst direction) and the angle of incidence +θ (the second direction) asseen in FIG. 2.

As this pixel 100 is arranged among the plurality of pixels of the imagesensor, it detects the directions of rays of light entering the imagesensor (the first direction and the second direction) so that thedistance between the subject and the imaging area can be measured bymeans of a method that will be described hereinafter.

Note that the angle of incidence −θ (the first direction) and the angleof incidence +θ (the second direction) of incident light need to beseparated clearly in order to make the image sensor show a precisedistance measuring performance.

More specifically, the light-receiving sensitivity of the pixel 100needs to be sufficiently higher relative to incident light from thesecond direction than relative to incident light from the firstdirection.

For this reason, the pixel 100 of this embodiment of the presentinvention is formed in such a way that the first optical waveguide andthe second optical waveguide of the optical waveguide are arranged inseries in the direction of propagation of light and the first and secondcore regions are formed by respective materials that make the refractiveindex of the second core region 113 higher than the refractive index ofthe first core region 112 and satisfy the requirement of therelationship of formula 1 shown below.n3>n1  (formula 1)

Note that the first core region 112 and the first clad region 122 of thefirst optical waveguide 102 show respective refractive indexes of n1 andn2, while the second core region 113 and the second clad region 123 ofthe second optical waveguide 103 show respective refractive indexes ofn3 and n4.

Since the clad regions showing the respective refractive indexes of n2and n4 are both normally made of a silica-based material, the refractiveindex n2 and the refractive index n4 are substantially equal to eachother.

Then, the light-receiving sensitivity of the pixel 100 varies remarkablyas a function of the angle of incidence of light and light coming fromthe first direction and light coming from the second direction can beclearly separated from each other. The reason for this will be describedbelow.

Normally, when the requirement of the above formula 1 is satisfied, theratio of the refractive index of the core region to that of the cladregion of the first optical waveguide 102 (n1/n2) is smaller than theratio of the refractive index of the core region to that of the cladregion of the second optical waveguide (n3/n4).

Generally, the number of guided modes that can exist in an opticalwaveguide is small when the ratio of the refractive index of the coreregion to that of the clad region of the optical waveguide is small.

As the number of guided modes is reduced, spatial separation ofelectromagnetic field modes among different guided modes becomesremarkable. Therefore, light coupled to different guided modes thatdiffer to correspond to the angles of incidence are spatially remarkablyseparated from each other.

Then, as a result, only incident light from the first direction can beefficiently blocked by arranging the light shielding member 105 at thelight exit end of the first optical waveguide 102.

Additionally, when the refractive index n3 of the second core region 113is made higher than the refractive index n1 of the first core region112, light propagated through the second optical waveguide 103penetrates into the clad region only with a short penetration depth sothat it is confined in the core region.

Thus, incident light from the second direction that is propagatedthrough the second optical waveguide is affected only to a small extentby the light scattering members and the light absorbing membersincluding the metal wiring 106 and the gate electrode 107 and hence canbe efficiently guided to the photoelectric conversion section 104. Atthe same time, the crosstalk noise to pixels around the pixel 100 due toscattering can be reduced.

As described above, the pixel 100 can be made to clearly separate lightfrom the first direction and light from the second direction byarranging the first optical waveguide 102 and the second opticalwaveguide 103 so as to satisfy the requirement of the relationship ofthe formula 1.

Thus, the distance can be measured precisely by using the pixel 100 asranging pixel.

In order to reduce the number of guided modes for improving the accuracyof distance measurement, the pixel size is reduced.

Generally, as the pixel size is reduced, the width of the core regionsof the optical waveguide is reduced correspondingly.

As the width of the core regions is reduced, the number of guided modesof the optical waveguide is reduced so that light from the firstdirection and light from the second direction can be clearly separatedfor the above-described reason.

Thus, as the pixel size is reduced, the light-receiving sensitivity ofthe pixel 100 varies remarkably as a function of the angle of incidenceof light. Then, as a result, the accuracy of distance measurement can beimproved.

If the wavelength of incident light is in the visible range, desirablythe unit length of a pixel is not greater than 2.5 μm.

More desirably, the unit length of a pixel is not greater than 2.0 μm.Most desirably, the unit length of a pixel is not greater than 1.5 μm.

In this embodiment, the light shielding member 105 is arranged in such away that the center position of the light shielding member 105 isshifted from the center axis of the pixel 100.

With this arrangement, light from the first direction can be efficientlyand selectively blocked.

Note, however, that the center position of the light shielding member105 may not necessarily be shifted from the center axis of the pixel100. In other words, a similar effect can be achieved by arranging thelight shielding member 105 in a central area and making the guided modesasymmetrical.

Then, the first optical waveguide is made to show a profile that isasymmetrical relative to the center axis of the pixel 100 in order tomake the guided modes asymmetrical. Alternatively, the refractive indexdistribution may be made asymmetrical.

The first optical waveguide 102 and the second optical waveguide 103 maynot necessarily be held in direct contact with each other. A film suchas an insulating film may be arranged between the first opticalwaveguide 102 and the second optical waveguide 103.

A member made of a material showing a refractive index higher than therefractive index of the core region of the first optical waveguide andlower than the refractive index of the core region of the second opticalwaveguide may be arranged between the first core region 112 and thesecond core region 113 in order to improve the light-receivingsensitivity relative to incident light from the second direction.

Then, the refractive index changes mildly between the first core regionand the second core region to raise the coupling efficiency betweenlight being propagated through the first optical waveguide and thesecond optical waveguide.

As a result, the light-receiving sensitivity of the ranging pixel can beimproved. Note, however, that the member of the above-described materialmay be buried in the core regions or provided as a film covering thecore regions and the clad regions.

Now, the method of measuring the distance between the subject and theimaging area by means of the image sensor of this embodiment will bedescribed below by referring to FIG. 3.

As shown in FIG. 3, imaging lens 201 forms an image of an externalsubject on the imaging area of the image sensor 200.

The image sensor 200 has a second pixel region provided with a pluralityof pixels (second pixels) 100 for detecting incident light from thesecond direction shown in FIG. 1 and a first pixel region provided witha plurality of pixels (first pixels) for detecting incident light fromthe first direction. FIG. 3 illustrates the optical axis 203 of theimaging lens 201.

Note that the pixels for detecting light entering from the firstdirection may be arranged in such a way that they take a postureobtained by turning the pixel 100 shown in FIG. 1 by 180°.

Then, the fluxes of light that pass through different regions on thesurface of the exit pupil of the imaging lens 201 strike the imagingarea of the image sensor 200 as fluxes of light showing different anglesof incidence because the imaging lens 201 and the image sensor 200 areseparated by a long distance relative to the pixel size.

The pixels 100 included in the second pixel region mainly detect thefluxes of light that pass through the region 204 corresponding to thesecond direction (the second exit pupil region) of the exit pupil (theexit pupil of the optical system for forming a subject image) of theimaging lens 201.

Similarly, the pixels included in the first pixel region mainly detectthe fluxes of light that pass through the region 202 corresponding tothe first direction (the first exit pupil region) of the exit pupil ofthe imaging lens 201.

Thus, the images of light passing through different regions on thesurface of the exit pupil of the imaging lens can be detected. Then, thepixel signal from the first pixel region and the pixel signal from thesecond pixel region are compared.

Then, with a known method, the distance between the subject and theimaging area of the image sensor can be detected when a ranging signalof the subject is output.

With the above-described manner, the light-receiving sensitivityrelative to light entering from a specific angle is improved so thatlight passing through a specific region on the plane of the pupil can beselectively received to precisely measure the distance.

Now, a numerical example will be described below.

FIG. 4 shows the configuration of the pixel 100, illustrating thenumerical example.

With this numerical example, the first core region and the second coreregion are respectively made of an organic material and TiO₂ so as toshow refractive indexes of 1.60 and 2.00.

Both the first clad region and the second clad region are made of asilica-based material so as to show a refractive index of 1.45.

FIG. 5 (line 1) shows the light-receiving sensitivity characteristic ofthe photoelectric conversion section that varies as a function of theangle of incidence of light. For the purpose of comparison, FIG. 5 alsoshows the light-receiving sensitivity characteristic of thephotoelectric conversion section that is obtained when both therefractive index of the first core region and that of the second coreregion are 1.60 (line 2) and the light-receiving sensitivitycharacteristic of the photoelectric conversion section that is obtainedwhen both the refractive index of the first core region and that of thesecond core region are 2.00 (line 3).

From FIG. 5, it will be seen that the light-receiving sensitivity ishigh at the negative side of the angle of incidence (the firstdirection) when the first core region shows a refractive index of 2.00(line 3 in FIG. 5).

For this reason, light entering at the positive side of the angle ofincidence (the second direction) and light entering at the negative sideof the angle of incidence (the first direction) cannot satisfactorily beseparated from each other.

When, on the other hand, the first core region is made to show arefractive index of 1.60 (line 1 in FIG. 5), the light-receivingsensitivity is low at the negative side of the angle of incidence (thefirst direction).

Then, light from the positive side of the angle of incidence (the seconddirection) and light from the negative side of the angle of incidence(the first direction) can be selectively received.

From FIG. 5, it will also be seen that, when the second core region ismade to show a refractive index of 1.60 (line 2 in FIG. 5), thelight-receiving sensitivity to light from the positive side of the angleof incidence (the second direction) is low if compared with when thesecond core region is made to show a refractive index of 2.00 (line 1 inFIG. 5).

This is because light that is propagated through the second opticalwaveguide is not affected significantly by scattering and absorption dueto the wiring and hence highly efficiently led to the photoelectricconversion section when the second core region is made to show a highrefractive index.

Thus, light entering at the positive side of the angle of incidence (thesecond direction) and light entering at the negative side of the angleof incidence (the first direction) can satisfactorily be separated fromeach other by the photoelectric conversion section when the second coreregion is made to show a high refractive index.

From the above, with the arrangement according to the present invention(line 1 in FIG. 5), the first direction and the second direction can beclearly separated from each other and, as a result, the distance can bemeasured highly precisely.

Second Embodiment

Now, the second embodiment of solid state image sensor according to thepresent invention will be described below by referring to FIG. 6.

FIG. 6 denotes a pixel 300 having a distance measuring function that isarranged in a part of the solid state image sensor of this embodiment.

The pixel 300 of the second embodiment differs from the pixel 100 of thefirst embodiment in that the pixel 300 has a first photoelectricconversion section 301 and a second photoelectric conversion section 302that are independent from each other.

The pixel 300 of the second embodiment also differs from the pixel 100of the first embodiment in that the second optical waveguide 103 isformed by using two core regions (the first core region 303, the secondcore region 304) instead of arranging a light shielding member 105 atthe light exit end of the first optical waveguide 102.

Then, the first core region 303 of the second optical waveguide 103 isarranged right above the first photoelectric conversion section 301,while the second core region 304 of the second optical waveguide 103 isarranged right above the second photoelectric conversion section 302.

Besides, wiring 106 for controlling the signals of the firstphotoelectric conversion section 301 and the second photoelectricconversion section 302, the gate electrode 107 shown in FIG. 1 and so onare arranged appropriately in the clad region of the first opticalwaveguide 102, the clad region of the second optical waveguide 103 andso on.

The electromagnetic modes that are spatially separated by the firstoptical waveguide 102 are selectively detected at the firstphotoelectric conversion section 301 and the second photoelectricconversion section 302 by way of the first core region 303 and thesecond core region 304 of the second optical waveguide.

The first core region 303 of the second optical waveguide has a functionof efficiently guiding light with the angle of incidence +θ (the seconddirection) to the first photoelectric conversion section 301 in aselective manner.

The second core region 304 of the second optical waveguide has afunction of effectively guiding light with the angle of incidence −θ(the first direction) to the second photoelectric conversion section 302in a selective manner.

The refractive index of the core region 112 of the first opticalwaveguide is made lower than the refractive index of the first coreregion 303 and that of the second core region 304 of the second opticalwaveguide.

With the above-described arrangement, the guided modes can be spatiallyseparated by the first optical waveguide according to the angle ofincidence and light can be efficiently guided to the first photoelectricconversion section 301 and the second photoelectric conversion section302 by way of the first core region 303 and the second core region 304of the second optical waveguide as in the case of the first embodiment.

Then, the distance can be precisely measured by arranging the firstphotoelectric conversion section 301 for selectively receiving lightfrom the second direction and the second photoelectric conversionsection 302 for selectively receiving light from the first direction ina plurality of pixels of the image sensor.

In this embodiment, the second optical waveguide 103 is made to have twocore regions including the first core region 303 and the second coreregion 304. However, the second optical waveguide 103 may notnecessarily have two core regions and may alternatively have four coreregions or a different number of core regions to function in a similarway.

Third Embodiment

A process of manufacturing a solid state image sensor having a pixel 100as shown in FIG. 1 will be described below by referring to FIGS. 7Athrough 7G for the third embodiment of the present invention.

Firstly, a silicon oxide film (not shown) is formed on the surface of asilicon substrate 108 by thermal oxidation. Then, a resist mask ofphotoresist is formed at a predetermined position and impurity ions areimplanted in order to form a photoelectric conversion section 104 in thesilicon substrate 108. Thereafter, the resist mask is removed typicallyby asking. Subsequently, a diffusion layer (not shown) is formed also byion implantation, using a similar technique (FIG. 7A).

Furthermore, a polysilicon film is formed to form a gate electrode 107for transferring the electric charge generated in the photoelectricconversion section 104.

Then, a gate electrode 107 is formed by etching the polysilicon to apredetermined pattern by means of a photolithography technique.

Thereafter, an interlayer insulating layer of BPSG (boron phosphorsilicate glass), for example, is formed on the silicon substrate 108 andthe gate electrode 107 and an operation of planarization is conducted bymeans of a CMP (chemical mechanical polishing) method (FIG. 7B).

Then, connection holes such as contact holes are formed through theinterlayer insulating layer for electric connections to other metalwirings. Similarly, a first wiring 106 a is formed and covered by theinterlayer insulating layer (FIG. 7C).

Subsequently, a resist mask of photoresist is formed at a predeterminedposition and the interlayer insulating layer is etched typically by dryetching in order to form a core region 113 in the second opticalwaveguide (FIG. 7D)

Furthermore, substances showing a high refractive index such as SiN andTiO₂, for example, are buried in the etched region typically by CVD andthen an operation of planarization is conducted by means of a CMP method(FIG. 7E).

The core region 113 of the second optical waveguide is desirably made ofan inorganic material that scarcely influences the subsequent processingsteps.

Then, a light shielding member 105 and a second wiring 106 b are formedlike the first wiring 106 a and covered by the interlayer insulatinglayer 122 such as SiO₂ or BPSG (FIG. 7F).

Then, a resist mask of photoresist is formed at a predetermined positionand etched typically by dry etching to produce, if necessary, a taperedprofile in order to form a core region 123 in the first opticalwaveguide. Furthermore, an organic material showing a high refractiveindex is buried into the etched region (FIG. 7G).

The core region 123 of the first waveguide is desirably formed by usingan organic material in order to produce only few air voids, when it isburied in a region showing a tapered profile and a high aspect ratio.

Then, if necessary, a color filter is formed (not shown).

While the first embodiment through the third embodiment are describedabove as so many front surface type CMOS solid state image sensors, thepresent invention is equally applicable to rear surface type CMOS solidstate image sensor by using similar optical waveguides.

Furthermore, the present invention is equally applicable to solid stateimage sensors of other types such as CCD solid state image sensors.

Fourth Embodiment

In this embodiment, a solid state image sensor according to the presentinvention is utilized as the image sensor of a digital camera.

FIG. 8 is a schematic illustration of a digital camera of the presentembodiment.

FIG. 8 illustrates an imaging lens 801, a solid state image sensor 802according to the present invention and an arithmetic processing section803. An image of a subject is formed in the solid state image sensor 802by way of the imaging lens 801 and an arithmetic process is executed bythe arithmetic processing section 803 on the basis of the electricsignals generated in the solid state image sensor. Then, an image to bedisplayed is formed.

Since a solid state image sensor according to the present invention canhighly precisely measure distances, the camera of this embodiment canoperate for high speed and high precision auto-focusing so that thecamera can acquire a high definition image when picking up a movingpicture.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2010-264609, filed Nov. 29, 2011, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A solid state image sensor having a plurality ofranging pixels, each of the ranging pixels including: a photoelectricconversion section for converting light into an electric signal; anoptical waveguide including a core region and a clad region arranged ata light-receiving side of the photoelectric conversion section; and alight shielding member in the optical waveguide, wherein the opticalwaveguide has at least two optical waveguides including a first opticalwaveguide and a second optical waveguide, wherein the second opticalwaveguide is arranged closer to a side of the photoelectric conversionsection than the first optical waveguide, in a direction extending awayfrom the side of the photoelectric conversion section, wherein a coreregion of the first optical waveguide has a refractive index lower thana refractive index of a core region of the second optical waveguide, andwherein the light shielding member is arranged between the core regionof the first optical waveguide and the core region of the second opticalwaveguide.
 2. The solid state image sensor according to claim 1, whereina center position of the light receiving member is shifted relative to acenter axis of the ranging pixel.
 3. The solid state image sensoraccording to claim 1, wherein the core region of the first opticalwaveguide is formed by using an organic material.
 4. The solid stateimage sensor according to claim 1, wherein the core region of the secondoptical waveguide is formed by using an inorganic material.
 5. The solidstate image sensor according to claim 1, further comprising a memberhaving a refractive index higher than the refractive index of the coreregion of the first optical waveguide and lower than the refractiveindex of the core region of the second optical waveguide, wherein themember is arranged between the first optical waveguide and the secondoptical waveguide.
 6. The solid state image sensor according to claim 1,wherein the first optical waveguide has a profile that is asymmetricalrelative to the center axis of the ranging pixel.
 7. The solid stateimage sensor according to claim 1, wherein the light shielding memberselectively shields an incident light in a first direction, and whereinthe second optical waveguide selectively guides an incident light in asecond direction different form the first direction to the photoelectricconversion section.
 8. A camera comprising an imaging lens, a solidstate image sensor and an arithmetic processing section, the solid stateimage sensor being one according to claim 1.